Recent progress in optical oxygen sensor instrumentation

Optical methods for the determination of dissolved or gaseous oxygen are mainly based on the principle of fluorescence quenching. Measurement schemes have been reported which employ various oxygen-sensitive dyes and bulky instrumentation. Typically, expensive fluorescence spectrometers or fibre-optic photometers have been used, and the applicability of such instruments is rather limited. A system based on low-cost semiconductor devices (light-emitting diodes (LEDS), photodiodes, low-cost analogue and digital components) and new LED-compatible oxygen-sensitive membranes has been developed at our institute. The instrument is capable of determining dissolved or gaseous oxygen and may be calibrated, for example, by a simple two-point calibration procedure with air-saturated and oxygen-free water. Thermostatization of the flow-through cell results in higher measurement accuracy and in a reduced influence of the ambient temperature on the instrument. The overall performance of the oxygen sensor has been investigated, e.g. measurement stability, effectivity of thermostatization, calibration, oxygen diffusion into the measuring cell and excitation feed-through.